The present invention relates to an X-ray image detecting apparatus, and more particularly to such an apparatus having its X-ray receiving plane composed of a two-dimensional array of X-ray sensors each of which constitutes a unit X-ray detector together with accompanying electronic elements.
Conventionally, an X-ray image is generally detected either with an X-ray camera using an X-ray film or with an apparatus devised so as to record on a tape recorder an X-ray image received by a TV camera through an X-ray image intensifier. The former method disadvantageously needs a long time to finally provide the picture of a detected X-ray image, while the latter, though more advantageous than the former in the rapidity of image detection, has an important disadvantage that the dynamic range of the X-ray image intensifier is smaller than that of a general X-ray image to be detected, resulting in the deterioration of the quality of the picture obtained from the X-ray image.
To overcome the disadvantages mentioned above, there has been provided a method in which X-ray receiving plane consists of a two-dimensional array, for example, of X-ray scintillators as X-ray sensors constituting picture elements, and the outputs from the scintillators are converted to electric signals and then recorded as a picture signal on a tape recorder. Each of the X-ray scintillators for detecting irradiated X-ray photons constitutes a unit X-ray detector together with a semiconductor photosensor for converting the optical scintillator output to corresponding electric pulse signals and a counter for counting the pulses outputted from the photosensor. Many such unit X-ray sensors are assembled in the form of a LSI (Large Scale Integrated Circuit) with their scintillator parts arranged in a two-dimensional array, on which an X-ray image is projected. However, this method necessitates some means for correcting the brightness irregularity which may appear, unless corrected, on an obtained picture owing to the sensitivily variations of the individual unit X-ray detectors, namely, of the scintillators and photosensors contained in the detectors. In a conventional typical method of correcting such brightness irregularity, a standard X-ray image with a uniform intensity throughout the entire X-ray receiving area is detected and recorded in the beginning for obtaining data of standard brightness irregularity, which data are to be used for correcting the brightness irregularity of the picture obtained from a general X-ray image to be detected. However, practising such a conventional method of correcting brightness irregularity needs a computer to perform the arithmetic operations necessary to properly display a detected image. The incorporation of a computer not only necessitates a long time to obtain a picture of the detected image because of the process of arithmetic operations for correcting the brightness irregularity, but also increases the entire cost of the apparatus.